The purpose of this study is to evaluate the effect of ritonavir/saquinavir on the metabolism of methadone. Given that approximately 35% of all AIDS cases are associated with injection drug use, it is imperative to know the drug-to-drug interaction in order to prescribe methadone concurrently with the protease inhibitors. Patients will be admitted to the GCRC for 24 hour pharmacokinetic samples of methadone.